Apparatus and method relating to tongs, continous circulation and to safety slips

ABSTRACT

A tong system includes an upper tong having grips for gripping a tubular and a rotation mechanism to rotate the grips and the tubular. A lower tong also has grips and a rotation mechanism to rotate the grips to provide rotation to a lower tubular, such that the upper and lower tubulars may be made up/broken out from one another, also so that string of tubulars may be rotated for drilling purposes without requiring a rotary table. Also, an apparatus and method for circulating fluid through a tubular string has a first fluid conduit for supplying fluid to the bore of an upper tubular to be made up into or broken out from the tubular string and a second fluid conduit for supplying fluid to the bore of the tubular string, which allows continuous circulation of fluid to occur whilst running the string into/pulling the string from, a borehole and also whilst making up tubulars into/breaking out tubulars from the string. Also, an upper seal for sealing about a portion of the outer circumference of a tubular to be made up onto or broken out from the string and a lower seal means for sealing about a portion of the outer circumference of the string, where the upper seal is an elastomeric ring which has an inner diameter substantially the same as the outer diameter of the tubular. Also, a valve mechanism includes a rotatable plate member and at least one bore. The plate member is moveable between obturation and non-obturation of the tubular. Also, a safety slip to prevent at least one tubular slipping therein has first and second arrangements of grips which are coupled to one another, preferably by a biasing mechanism.

The present invention relates to an apparatus and method of drillingboreholes in the ground or subsea surface, and also to an apparatus andmethod for use in workovers, well maintenance and well intervention, andparticularly, but not exclusively relates to apparatus and method foruse in hydrocarbon exploration, exploitation and production, but couldalso relate to other uses such as water exploration, exploitation andproduction.

Conventional drilling operations for hydrocarbon exploration,exploitation and production utilise many lengths of individual tubularswhich are made up into a string, where the tubulars are connected to oneanother by means of screw threaded couplings provided at each end.Various operations require strings of different tubulars, such as drillpipe, casing and production tubing.

The individual tubular sections are made up into the required stringwhich is inserted into the ground by a make up/break out unit, where thenext tubular to be included in the string is lifted into place justabove the make up/break out unit. A first conventional method of doingthis uses a single joint elevator system which attaches or clamps ontothe outside surface of one tubular section and which then lifts thisupwards. A second conventional method for doing this utilises a liftnubbin which comprises a screw thread which engages with the box end ofthe tubular such as drill pipe, and the lift nubbin and tubular arelifted upwards by a cable. However, this second method in particular canbe relatively dangerous since the lift nubbin and tubular will tend tosway uncontrollably as they are being pulled upwards by the cable.

From a second aspect, conventional drilling rigs utilise a make up/breakout system to couple/decouple the tubular pipe sections from the tubularstring. A conventional make up/break out system comprises a lower set oftongs which are brought together to grip the lower pipe like a vice, andan upper set of tongs which firstly grip and then secondly rotate theupper pipe relative to the lower pipe and hence screw the two pipestogether. In addition to this conventional make up/break out system, aconventional drilling rig utilises a rotary unit to provide rotation tothe drill string to facilitate drilling of the borehole, where theconventional rotary unit is either a rotary table provided on the drillrig floor or a top drive unit which is located within the drilling rigderrick.

According to a first aspect of the present invention there is providedan apparatus for handling tubulars, the apparatus comprising

-   a pair of substantially vertical tracks;-   a rail mechanism movably connected to each track; and-   a coupling mechanism, associated with the rail mechanism, for    coupling to a tubular; and-   a movement mechanism to provide movement to the rail mechanism.

According to a second aspect of the present invention there is provideda method of handling tubulars, the method comprising:

-   providing a rail mechanism, the rail mechanism being associated with    a coupling mechanism for coupling to a tubular, and the rail    mechanism being movably connected to a substantially vertical track;-   coupling the coupling mechanism to a tubular; and-   operating a movement mechanism to move the rail mechanism.

The substantially vertical tracks are preferably secured to a framewhich is typically a derrick of a drilling rig. The pair ofsubstantially vertical tracks are preferably arranged about thelongitudinal axis of a borehole mouth, such that the pair of tracks andthe borehole mouth lie on a common plane, with one track at either sideof the borehole mouth.

Preferably, the rail mechanism is suitably connected to the respectivetrack by any suitable means such as runners or rollers and the like. Themovement mechanism may comprise a motive means associated with therunners or rollers and the like. Alternatively, the movement mechanismmay comprise a cable, winch or the like coupled at one end to the railmechanism and coupled at the other end to a motor and real arrangementor a suitable counterweight arrangement or a suitable counterbalancewinch hoisting or the like.

Preferably, the coupling mechanism comprises a suitable coupling forcoupling to the tubular, where the suitable coupling may comprise amember provided with a screw thread thereon for screw threadedengagement with one end of the tubular. Alternatively, the suitablecoupling may comprise a vice means to grip the end of the tubular.Alternatively, the suitable coupling may comprise a fluid swivel whichcouples directly to the end of the tubular, or indirectly to the end ofthe tubular via a kelly. Typically, the derrick may be provided with atubular rack for storing tubulars, and a ramp which may extenddownwardly at an angle from the lower end of the derrick toward thetubular rack, and a tubular guide track may also be provided at one orboth sides of the ramp.

According to a third aspect of the present invention there is providedan apparatus for handling a tubular, the apparatus comprising at leastone substantially vertical track;

-   a coupling mechanism, connected to the track, for coupling to a    tubular;-   a pair of moveable members which are hingedly connected to both the    coupling mechanism and the vertical track, such that movement of the    pair of moveable members results in movement of the coupling    mechanism substantially about a longitudinal axis of the track.

According to a fourth aspect of the present invention there is provideda method of handling a tubular, the method comprising providing at leastone substantially vertical track;

-   connecting a coupling mechanism to the track, the coupling mechanism    for coupling to a tubular;-   providing a pair of moveable members which are hingedly connected to    both the coupling mechanism and the vertical track; and-   moving the pair of moveable members to move the coupling mechanism    substantially about a longitudinal axis of the track.

Preferably, a rail mechanism is provided and which is movably connectedto the track, and typically, the coupling mechanism is associated withthe rail mechanism. More preferably, the pair of movable members arehingedly connected to both the coupling mechanism and the railmechanism.

Preferably, there are a pair of substantially vertical tracks, and thesubstantially vertical tracks are preferably secured to a frame which istypically a derrick of a drilling rig. The pair of substantiallyvertical tracks are preferably arranged about the longitudinal axis of aborehole mouth, such that the pair of tracks and the borehole mouth lieon a common plane, with one track at either side of the borehole mouth.Typically, the movement of the pair of movable members results inmovement of the coupling mechanism substantially about the longitudinalaxis of the track such that a longitudinal axis of a tubular coupled tothe coupling mechanism is substantially coincident with the longitudinalaxis of the borehole mouth.

Preferably, a motive means is provided to permit movement of the pair ofmoveable members, where the motive means may be a suitable motor such asa hydraulic motor.

According to a fifth aspect of the present invention, there is provideda tong apparatus, the tong apparatus comprising:

-   an upper tong having a gripping means for gripping a tubular, the    upper tong further comprising a rotation mechanism to provide    rotation to the gripping means to provide rotation to said tubular;    and-   a lower tong having a gripping means for gripping a tubular, the    lower tong further comprising a rotation mechanism to provide    rotation to the gripping means to provide rotation to said tubular.

According to a sixth aspect of the present invention, there is provideda method of providing rotation to at least one tubular, the methodcomprising:

-   providing an upper tong having a gripping means for gripping a    tubular, the upper tong further comprising a rotation mechanism to    provide rotation to the gripping means;-   providing a lower tong having a gripping means for gripping a    tubular, the lower tong further comprising a rotation mechanism to    provide rotation to the gripping means; and-   operating at least the rotation mechanism of the upper tong to    provide rotation to said tubular.

Preferably, the method further comprises operating the rotationmechanism of the lower tong to provide rotation to said tubular.

Typically, the upper tong comprises a plurality of gripping means.Preferably, a range of gripping means can be utilised to grip differingdiameters of tubulars.

Preferably, a motive means is provided to actuate the rotationmechanism, where the motive means may be a hydraulic motor having asuitable hydraulic fluid power supply.

Preferably, the lower tong comprises a plurality of gripping means.Preferably, a range of gripping means can be utilised to grip differingdiameters of tubulars. Preferably, a motive means is provided to actuatethe rotation mechanism, where the motive means may be a hydraulic motorhaving a suitable hydraulic fluid power supply. Preferably, the lowertong further comprises a turntable bearing means which support ring gearof the gripping means. Typically, the lower tong further comprises abreaking system which permits controlled release of residual tubularstring torque.

Preferably, a travelling slip mechanism is also provided and which iscapable of engaging at least a portion of the outer circumference of atubular string, and preferably, the travelling slip is capable of beingrotated with respect to the derrick by means of a rotary bearingassembly mechanism. Typically, the travelling slip is provided with avertical movement mechanism which can be actuated to move the travellingslip and the engaged tubular string in one or both vertical directions.

According to a seventh aspect of the present invention, there isprovided an apparatus for circulating fluid through a tubular string,the string comprising at least one tubular, the apparatus comprising:

-   a first fluid conduit for supplying fluid to the bore of an upper    tubular to be made up into or broken out from the tubular string;    and-   a second fluid conduit for supplying fluid to the bore of the    tubular string.

According to an eighth aspect of the present invention, there isprovided a method of circulating fluid through a tubular string, thestring comprising at least one tubular, the method comprising:

-   providing a first fluid conduit for supplying fluid to the bore of    an upper tubular to be made up into or broken out from the tubular    string; and-   providing a second fluid conduit for supplying fluid to the bore of    the tubular string.

Preferably, the first fluid conduit is releasably engageable with anupper end of the upper tubular. Preferably, the first fluid conduit isprovided with a valve mechanism which can be operated to permit the flowof fluid into or deny the flow of fluid into the first fluid conduitand/or upper end of the tubular.

Preferably, one end of the second fluid conduit is in fluidcommunication with a chamber, and typically, the second fluid conduit isprovided with a valve mechanism which can be operated to permit the flowof fluid into, or deny the flow of fluid into, the second fluid conduitand/or the chamber.

Preferably, the chamber is adapted to permit a tubular to be made upinto, or broken out from, a tubular string. The chamber typicallycomprises a bore, which is preferably arranged to be substantiallyvertical, and is more preferably arranged to be coincident with thelongitudinal axis of the mouth of the borehole. Typically, the chambercomprises an upper port into which the said tubular can be inserted intoor removed from the chamber. Preferably, a valve mechanism is providedand is actuable to seal the bore of the chamber, typically at a locationbelow the upper port. Preferably, an upper seal is provided, where theupper seal is preferably located above the said location, and where theupper seal is arranged to seal around at least a portion of thecircumference of the said tubular. Typically, a lower seal is provided,where the lower seal is preferably located below the said location, andwhere the lower seal is arranged to seal around at least a portion ofthe circumference of the tubular string.

Preferably, a valve system comprising one or more further valves isprovided to control the supply of fluid to the first fluid conduit valvemechanism and second fluid conduit mechanism.

Typically, the method comprises the further steps of inserting the lowerend of the upper tubular into the upper port, where the valve mechanismtypically denies the flow of fluid into the first fluid conduit. At thispoint, the valve mechanism seals the bore of the chamber. Thereafter,the upper seal seals around at least a portion of the circumference ofthe tubular, and the valve mechanism of the second fluid conduit isoperated to permit the flow of fluid into the chamber, preferably at alocation below the valve mechanism sealing the bore of the chamber, suchthat fluid flows into the upper end of the tubular string.

The method preferably comprises the further steps of operating the valvemechanism to permit the flow of fluid into the first fluid conduit andupper end of the tubular. Preferably, thereafter, the valve mechanism isactuated to open the bore of the chamber, and thereafter, the valvemechanism is operated to deny the flow of fluid into the second fluidconduit. Thereafter, the tubular is preferably made up into the tubularstring, and thereafter, the first fluid conduit is typically releasedfrom engagement with the upper end of the upper tubular.

According to a ninth aspect of the present invention, there is providedan apparatus for providing a seal between a tubular to be made up in toor broken out from a tubular string, the tubular string comprising atleast one tubular, the apparatus comprising:

-   an upper seal means for sealing about a portion of the outer    circumference of the said tubular to be made up onto or broken out    from the string;-   a lower seal means for sealing about a potion of the outer    circumference of the string; and-   the upper seal comprising an elastomeric ring which is adapted to    have an inner diameter substantially the same as the outer diameter    of at least a portion of the tubular.

Preferably, the elastomeric ring is formed from a suitable material suchas rubber. Typically, the lower seal also comprises an elastomeric ringwhich is adapted to have an inner diameter substantially the same as theouter diameter of at least a portion of tubular string.

According to a tenth aspect of the present invention there is provided avalve mechanism for use in providing a seal between two tubulars, thevalve mechanism comprising:

-   a plate member which is capable of rotation about an axis;-   at least one bore formed through the plate member;-   the plate member being arranged such that it is capable of movement    between a first configuration in which a portion of the plate member    obturates the longitudinal axis of at least one of the tubulars; and-   a second configuration in which the bore is concentric with the    longitudinal axis of at least one of the tubulars.

According to an eleventh aspect of the present invention there isprovided a method of providing a seal between two tubulars, the methodcomprising:

-   providing a plate member which is capable of rotation about an axis;-   the plate member having at least one bore;-   wherein the plate member is capable of being rotated between a first    configuration in which a portion of the plate member obturates the    longitudinal axis of at least one of the tubulars; and-   a second configuration in which the bore is concentric with the    longitudinal axis of at least one of the tubulars.

Preferably, the plate member is capable of being rotated between a firstconfiguration from which a portion of the plate member obturates thelongitudinal axis of both of the tubulars, and a second configuration inwhich the bore is concentric with the longitudinal axis of both of thetubulars, both of the tubulars being concentric with one another.

Preferably, the plate member is arranged within a chamber, such that theradius of the plate member is perpendicular to the longitudinal axis ofboth tubulars. Preferably, the plate member is substantially circular,and more preferably, the centre axis of the plate member is off-centrewith respect to the longitudinal axis of both tubulars.

According to a twelfth aspect of the present invention, there isprovided an apparatus to prevent a tubular slipping therein, theapparatus comprising a first arrangement of grips adapted to grip thetubular, and a second arrangement of grips adapted to grip the tubular,characterised in that the first and second arrangements of grips arecoupled to one another.

Preferably the first and second arrangements of grips are coupled to oneanother by a coupling mechanism which is more preferably a biasingmechanism. Preferably the biasing mechanism is arranged to bias thefirst and second arrangements of grips away from one another. Preferablyat least one of or more preferably both of each of the first and secondarrangements of grips comprise a first and second portions wherein thefirst portion is coupled to the second portion by a tapered surface andpreferably a moveable locking mechanism, such that the first portion iscapable of moving with respect to the second portion along the taperedsurface.

Preferably the first arrangements of grips are located vertically belowthe second arrangements of grips and the first arrangements of gripscomprise a relatively large surface area for gripping the tubular andare the primary gripping arrangement.

Typically the second arrangement of grips comprise a relatively smallersurface area for gripping the tubular and provide a backup or safetygripping arrangement.

Preferably a lower face of the second arrangement of grips is coupled toan upper face of the first arrangement of grips and the upper face ofthe first arrangement of grips is of a larger surface area than a lowerface of the first arrangement of grips.

Preferably the first arrangement of grips comprise a stop means forpreventing movement of the second arrangement of grips in a direction,preferably radially, away from the tubular being gripped.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a drilling rig incorporating aspects ofthe present invention;

FIG. 2 is a portion of the drilling rig of FIG. 1 in a firstconfiguration;

FIG. 3 a is a portion of the drilling rig of FIG. 1 in a secondconfiguration;

FIG. 3 b is a more detailed perspective view of the portion of thedrilling rig of FIG. 3 a;

FIG. 4 is a front perspective view of a portion of the drilling rig ofFIG. 3 a;

FIG. 5 is a perspective view looking upwardly at the portion of thedrilling rig of FIG. 3 a;

FIG. 6 is a perspective view of a ramp and drill pipe loading area ofthe drilling rig of FIG. 1;

FIG. 7 a is a cross-sectional side view of the derrick of the drillingrig of FIG. 1;

FIG. 7 b is a front view of the derrick of FIG. 7 a;

FIG. 8 a is a cross-sectional more detailed view of a portion of theapparatus of FIG. 8 b;

FIG. 8 b is a front cross-sectional view of a portion of the derrick ofthe drilling rig of FIG. 1;

FIG. 9 a is a cross-sectional more detailed view of a portion of thederrick of FIG. 9 b;

FIG. 9 b is a front cross-sectional view of the derrick of the drillingrig of FIG. 1;

FIG. 10 a is a more detailed view of a portion of the apparatus of FIG.10 b;

FIG. 10 b is a front view of the derrick of FIG. 1;

FIG. 11 a is a more detailed view of a portion of the apparatus of FIG.11 b;

FIG. 11 b is a front view of the derrick of FIG. 1;

FIG. 12 a is a side view of the derrick of FIG. 1;

FIG. 12 b is a front view of the derrick of FIG. 1;

FIG. 13 a is a side view of the derrick of FIG. 1;

FIG. 13 b is a front view of the derrick of FIG. 1;

FIG. 14 a is a more detailed view of the portion of the apparatus ofFIG. 14 b;

FIG. 14 b is a front view of the derrick of FIG. 1;

FIG. 15 a is a side view of the derrick of FIG. 1;

FIG. 15 b is a front view of the derrick of FIG. 1;

FIG. 16 a is a side view of the derrick of FIG. 1;

FIG. 16 b is a front view of the derrick of FIG. 1;

FIG. 17 a is a front view of upper and lower tongs mounted within asnubbing unit;

FIG. 17 b is a perspective view of a portion of the snubbing unit ofFIG. 17 a;

FIG. 17 c is a top view of a portion of the snubbing unit of FIG. 17 a;

FIG. 17 d is a rear view of a portion of the snubbing unit of FIG. 17 a;

FIG. 17 e is a side view of a portion of the snubbing unit of FIG. 17 a;

FIG. 18 is a more detailed part cross-sectional view of a portion of thesnubbing unit of FIG. 17 a;

FIG. 19 is a more detailed part cross-sectional view of the snubbingunit of FIG. 17 a;

FIG. 20 is a more detailed part cross-sectional view of a portion of thesnubbing unit of FIG. 17 a;

FIG. 21 is a more detailed part cross-sectional view of a portion of thesnubbing unit of FIG. 17 a;

FIG. 22 is a more detailed part cross-sectional view of a portion of thesnubbing unit of FIG. 17 a;

FIG. 23 is a perspective view of a valve plate of the snubbing unit ofFIG. 17 a;

FIG. 24 is a schematic view of the snubbing unit of FIG. 17 a showing acontinuous circulation configuration with a main valve closed;

FIG. 25 is a schematic view of the snubbing unit of FIG. 17 a in acontinuous circulation configuration with the main valve open;

FIG. 26 is a schematic view of the snubbing unit of FIG. 17 aincorporating a stripper design;

FIG. 27 is a schematic view of the snubbing unit of FIG. 17 aincorporating a ram design in a first configuration;

FIG. 28 is a schematic view of the snubbing of FIG. 17 a incorporation aram design in a second configuration;

FIG. 29 is a cross-sectional view of a first embodiment of a safety slipmechanism, in accordance with a twelfth aspect of the present invention,in an open configuration;

FIG. 30 is a cross-sectional view of the safety slip mechanism of FIG.29 in a closed configuration;

FIG. 31 is a cross-sectional view of a portion of the safety slipmechanism of FIG. 29;

FIG. 32 is a half cross sectioned view of a second embodiment of asafety slip mechanism, in accordance with the twelfth aspect of thepresent invention, in a closed configuration;

FIG. 33 is a cross-sectional view of the second embodiment of the safetyslip mechanism of FIG. 32, but in an open configuration; and

FIG. 34 is a cross-sectional plan view of the safety slip mechanism ofFIG. 33 through section C—C.

FIG. 1 shows a drilling rig generally designated at 100. The drillingrig 100 is particularly suited for use in the business of exploration,exploitation and production of hydrocarbons, but could also be used forthe same purposes for other gases and fluids such as water. With regardto hydrocarbons, the drilling rig 100 can be used for operations suchas, but not limited to, snubbing, side tracks, under balanced drilling,work overs and plug and abandonments. The drilling rig 100 can beutilised for land operations (as shown in FIG. 1) as well as in marineoperations since it can be modified to be installed on an offshoredrilling rig, a drill ship or other floating vessels.

The drilling rig 100 comprises a derrick 102 which extends verticallyupwardly from a rig floor 8, where the rig floor 8 is carried by asuitable arrangement of supports 104 which are secured by appropriatemeans to the ground 1 or floating vessel top side 1.

As can be seen in FIGS. 1 to 4 and 6, the drilling rig 100 optionallyincludes a ramp 5 which extends downwardly at an angle from the rigfloor 8. The ramp 5 can be used by personnel as an evacuation slide 5 ifit is required that the personnel quickly evacuate the drilling rig 100.A drill pipe guide track 7 a, 7 b is located at each side of the slide 5and which fully extends from the drill rig floor 8 to the ground 1. Adrill pipe rack 6 a, 6 b is located at the outer side of each respectivedrill pipe guide track 7 a, 7 b, where the rack 6 a, 6 b is capable ofholding a plurality of tubular drill pipe lengths, such as drill pipe17. Each rack 6 a, 6 b comprises two or more kickover troughs (notshown) spaced along the length of the rack 6 a, 6 b, where the troughscan be operated to move lengths of drill pipe 17 from the rack 6 a, 6 bto the respective track 7 a, 7 b or vice versa as required, and do thisby being angled either respectively inwardly or outwardly byapproximately two or three degrees either way. A rope or counterbalancewinch arrangement (not shown) is also provided for each pipe guide track7, such that the rope/winch arrangement can be operated to pull pipes 17from the lower end of the track 7 a, 7 b up to the drill rig floor 8.The rope/winch arrangement can also be operated to lower pipe 17 fromthe drill rig floor 8 to the lower end of the track 7 a, 7 b.

It should however be noted that the downwardly angled fire evacuationslide 5 is an optional feature of the drilling rig 100.

FIG. 1 also shows an arm runner 9 a, 9 b being moveably located on arespective derrick dolly track 4 a, 4 b. As shown in FIGS. 3 b, 7 a and8 b for example, each arm runner 9 a, 9 b is provided with a pair ofarticulated pipe arms 12 which are hingedly attached at one end to therespective arm runner 9 a, 9 b and are hingedly attached at the otherend to a respective pipe handler fluid swivel 13 a, 13 b. Thisarrangement allows the fluid swivel 13 a, 13 b to be moved, by means ofsuitable motors (not shown), inwardly from the plane parallel to thelongitudinal axis of the respective dolly track 4 a, 4 b to the planeparallel with the longitudinal axis of the borehole, such that thearticulated pipe arms 12 act like a collapsible parallelogram. Arespective goose neck pipe 18 a, 18 b is provided at the upper end ofthe respective fluid swivel 13 a, 13 b and is in sealed fluidcommunication with the internal bore of the respective fluid swivel 13a, 13 b. A suitable pipe end coupling is provided at the lower end ofeach fluid swivel 13, where this pipe end coupling may suitably be ascrew thread coupling for connection with the box end of a drill pipe17. A wire pulley 10 a, 10 b is provided for each arm runner 9, and issecured at one end to the upper portion of the arm runner 9, where theother end of the wire pulley 10 is coupled to a suitablelifting/lowering mechanism, which may be a motor and reel arrangement,or may be a suitable counter weight arrangement, or may be a suitablecounter balance winch hoisting (not shown).

Alternatively however, the dolly tracks 4A, 4B of the derrick 102 couldbe modified to be the same as the dolly tracks of a conventional rig inwhich there will be a block (not shown) and top drive (not shown), andin this case the arm runners 9A, 9B are also suitably modified such thatthey can be used in conventional dolly tracks of a conventional rig.

A method of operating the pipe handling mechanism, in accordance with anaspect of the present invention, will now be described. Drill pipe 17 ais lifted up one of the guide tracks 7 a as previously described, untilthe upper end of the drill pipe 17 a is located in relatively closeproximity to the pipe coupling provided on the first pipe handler swivel13 a. The box end of the drill pipe 17 a is then coupled to the pipe endcoupling of the fluid swivel 13 a, such that the pipe handling mechanismis in the configuration shown in FIG. 2. The cable 10 a lifting/loweringmechanism is then operated such that the arm runner 9 a, and hence drillpipe 17 a is lifted upwardly to the configuration shown in FIGS. 1, 3 a,3 b, 4, 5, 7 a and 7 b, until the arm runner 9 a and hence drill pipe 17a are in the configuration shown in FIGS. 8 a and 8 b. It should benoted that it is preferred that the drill pipe 17 a is lifted upwardlyat a downwardly projecting angle, and this provides the advantage thatthe lower end of the drill pipe 17 a is kept well clear of the rig floor8.

However, it should be noted that the other arm runner 9 b and drill pipe17 b have already been moved in a similar manner, and the associatedmotor has been operated to move the drill pipe 17 b such that thearticulated pipe arms 12 have moved inward and the drill pipe 17 b isco-axial with the borehole.

A make up/break out unit will now be described for making up the drillstring, in accordance with the present invention.

A make up/break out unit in the form of a snubbing unit is generallydesignated at 20 and is shown in FIG. 17( a) as comprises a frame 106which is made up of a work basket base 106 a, support column spacers 106b, work basket support column 106 c, and snubbing unit base 106 d. Anupper tong 108 and a lower tong 109 are mounted within a tong frame 110which is further mounted within the work basket base 106 a as can beseen in FIG. 17 a, where the tong frame 110 can be seen in isolation inFIGS. 17 b to 17 e.

It should be noted that the upper tong 108 can be used to make up/breakout work strings, casing and production tubulars as large as 8⅝ inchesin diameter, although if modified in a suitable fashion, then it couldbe used for larger diameters if required.

The lower tong 109 is also known as a rotary back up 109, and is used torotate the drill string 17 at speed and torque required for milling,side tracking and drilling. However, the lower tong 109 also acts as aback up to the upper tong 108 when making up or breaking outconnections.

Another main component of the snubbing unit 20 is a rotary bearingassembly 112 which is coupled to the upper surface of a cylinder plate116. The moveable bearing of the rotary bearing 112 is secured to a setof travelling slips 114 which are used to engage the drill pipe 17, andhence the rotary bearing assembly 112 allows the travelling slips 114 torotate whilst the slips 114, as will subsequently be described, supportthe weight of the drill string to permit simultaneous vertical pipemanipulation and rotation of the work string. As will also be described,a hydraulic swivel or hydraulic bypass (not shown) is integrated intothe rotary bearing assembly 112 and allows the slips 114 to be remotelyoperated at all times and eliminate the need to make/break hoseconnections.

Mounting the tong system above the snubbing unit 20 travelling slips 114eliminates the need to swing tongs 108, 109 to engage and disengage thedrill pipe 17 at every drill pipe joint connection by allowing the drillpipe 17 and drill pipe joints to pass through the tongs 108, 109 duringtripping operations. The tongs 108, 109 and travelling slips 114 have amanually operated “large-bore” feature which allows their bore to bequickly increased to allow passage of downhole tools with diameters upto and over 11 inches. A remotely mounted control panel can be utilisedto operate all tong 108, 109 functions at any jack position withoutplacing personnel at dangerous positions, and this enhances safety andspeeds tripping operations.

Additionally, this has the advantage that operators will be able to makeup/break out connections while the drill pipe 17 is being moved by thesnubbing unit 20. It should be noted that reactive make up/break outtorques are transferred between the tongs 108, 109 via the frame 106 anda reaction column 118 (as shown in FIG. 17( a) and 14 (as shown in FIG.4), which is coupled to the frame 106 by means of a roller joint 120.Hence, the snubbing unit 20 can move vertically upwardly or downwardlyby means of the roller joint 120. Hydraulic jacking cylinders 122, ofwhich there are preferably four, are arranged, and act, between thestationary snubbing unit base 106 d and the moveable cylinder plate 116,and actuation of the hydraulic jacking cylinders 122 provides movementto the cylinder is plate 116 and hence snubbing unit 20.

FIG. 17 a also shows the location of fixed/stationary slips 124 as beingmounted to the upper section of the BOP stack 126, where the fixed slips124 and BOP stack 126 are stationary with respect to the drill rig floor8. Hence, the snubbing unit 20 is moveable by the hydraulic jackingcylinders 122 with respect to the fixed slips 124.

The active make up/break out torques are transferred between the uppertong 108 and lower rotary back up 109 by means of an integral reactioncolumn in the form of a closed head tong leg assembly 113 and thesubstructure of the derrick 102. This allows the snubbing unit 20 toaccept conventional hydraulic load cell and torque gauge assembliesand/or electronic load cells required for computerised tubular make upcontrol.

Reactive drilling torques will be transferred back to the derrick 102 bymeans of the reaction column 118 (shown if FIG. 3( b) as being securelymounted to the derrick 102) and roller joint 120. Hence, this rigidmounting system allows high speed work string rotation duringmilling/drilling operations with a minimum of rotating components, thesebeing the travelling slips 114 and a portion of the rotary bearingassembly 112, which reduces vibration and hazards associated withexposed rotating equipment.

The upper tong 108 will now be described in detail. The upper tong 108provides means to make up and break out tubing, casing or drill pipeduring tripping and snubbing operations, and is hydraulically powered.The upper tong 108 comprises three sliding jaws (not shown) whichvirtually encircle the drill pipe 17 to maximise torque while minimisingmarking and damage to the outer surface of the drill pipe 17. The uppertong 108 is provided with a cam operated jaw system (not shown) whichcan be opened to allow passage of work string tool joints as well astubing and casing couplings. A range of jaw systems can be used fordifferent dies such as dove tail strip dies which are used with drillpipe tool joints, and wrap around dies which are used with tubing orcasing. The upper tong 108 can also be used for running CRA tubulars(such as 13% to 26% Cr tubulars) with grit faced dies. Additionally,non-marking aluminium dies can also be used with low friction jaws.Additionally, electronic turns encoder(s) and electronic load cell(s)can be provided to permit torque turn compatibility with electronic OCTGanalysis systems, which can provide a record, such as a computer printout, of the quality of the make up between the respective end joints oftwo tubulars.

Additionally, it should be noted that the dies can be replaced whilstpipe passes through the upper tong 108. Also, the upper tong 108 can bemanually operated such that the tong bore can be increased to allowpassage of tools with diameters up to 11.06 inches. The upper tong 108is powered by twin two speed hydraulic motors (not shown) which providespeeds and torque capable of spinning and making/breaking high torqueconnections. The upper tong 108 is provided with a hydraulic powersupply which has a 35 gpm and 3000 psi output (62 hydraulic Horse Power)which produces 30,000 ft lbs at 9 rpm and high torque, low speed modeand 15,000 ft lbs at 18 rpm in low torque, high speed mode.

Alternatively, the hydraulic motors can provide 24 rpm maximum speed andlow torque, high speed mode at 47.6 gpm which is the maximum allowableflow rate using a standard PVG 120 Danfoss™ valve package, althoughalternative valve systems can be used to provide even higher speeds athigher flow rates. The upper tong 108 can be used for tubulars with arange from 2 1/16 inches to 8⅝ inches outside diameter with a range ofjaws and dies being supplied as required to accommodate the varyingdiameters. The gripping range for jaws being supplied with dove taildies is half an inch under the nominal size of the jaws, and thegripping range for jaws supplied with wrap around dies is that the wraparound dies are machined to match specific tubing, casing, tool joints,couplings or accessory diameters.

The lower tong or rotary back up 109 has two functions. During drillingoperations, the rotary back up 109 generates the torque required forhigh speed milling and drilling. This torque is transferred to the outerdiameter of the work or drill string 17 by means of three sliding jaws.During tripping operations, the jaws of the rotary back up 109 areactivated to grip the pipe 17 and resist the torque generated by theupper tong 108 when making up or breaking out the tubular connections.However, the rotary back up 109 differs from the upper tong 108 inseveral aspects. Firstly, the rotary back up 109 has large turntablebearings (not shown) to support the ring gear (not shown) instead of aseries of dumb bell roller assemblies (not shown) which are provided onthe upper tong 108. Also, the body of the rotary back up 109 is sealedand filled with gear oil to protect the bearings in gear surfaces duringextended periods of drilling. A hydraulically operated braking system(not shown) is also provided which allows controlled release of residualwork string torque. However, the rotary back ups 109 drive train (notshown) is similar to the drive train (not shown) of the upper tong 108,but features different motor displacements and gear ratios. However,like the upper tong 108, the rotary back up 109 utilises three jawswhich virtually encircle the pipe 17 to maximise torque whilstminimising marking and damage to the outer surface of the pipe 17. Thecam operated jaw system (not shown) of the rotary back up 109 can beopened to allow passage of tubing and casing couplings, and the rotaryback UP's 109 jaw systems (not shown) are interchangeable with those ofthe upper tong 108. Dovetail strip dies (not shown) can be provided forthe rotary back up's 109 jaws for use with drill pipe tool joints andwrap around dies can be used for tubing or casing. Additionally, thedies can be replaced while the drill pipe 17 passes through the rotaryback up 109, and the rotary back up 109 can be manually operated toincrease it's bore to allow the passage of tools with diameters up to11.06 inches. Twin two speed hydraulic motors (not shown) providesspeeds for milling and drilling operations. A removable lower pipe guideplate assembly (not shown) is provided separately for each specificcoupling diameter and assists pipe alignment during jacking operations.

The hydraulic power supply of the rotary back up 109 supplies 145 gpmand 2250 psi output (190 hydraulic horse power) and produces 7500 ft lbsat 80 rpm in high speed, low torque mode and 15000 ft lbs at 40 rpm inhigh torque, low speed mode.

The tubular capacity and the gripping range for the rotary back up 109is the same as that for the upper tong 108.

Referring again to FIG. 17( a), the tong frame 110 is bolted to thetravelling slips 114 via a lower tong frame 111, although it should benoted that some configurations may require a separate adapter plate (notshown). The upper tong 108 is suspended within the tong frame 111 bydouble acting spring assemblies located on legs 113 (see FIG. 17( b))which extend upward from the rotary back up 109. The upper tong 108 canbe pinned in one of two positions to facilitate make up of work stringtool joints and connections using couplings. The spring assemblies (notshown) within legs 113 allow the upper tong 108 to float ±2.5 inches toaccommodate thread lead during make up or break out. An open throat topguide plate 115 is fixed to the upper end of legs 113 and is fitted withlifting eyes 117 which enable handling of the tong frame 110. Anoptional remotely operated adjustable upper guide plate assembly can beprovided to facilitate hands off stabbing of tubulars, and hence theremotely operated adjustable upper guide plate assembly acts as ahydraulic stabbing guide for the tubulars. The tong frame 110 isapproximately 39 inches wide by 39 inches deep.

The rotary bearing assembly 112 allows the travelling slips 114 torotate under load while the pipe 17 is being manipulated. The rotarybearing assembly 112 is attached to the upper end of the cylinder plate116 of the snubbing unit 20 and features a flange (not shown) toaccommodate the travelling slip's 114 mounting bolts (not shown). Theseloads are transferred into a large diameter turntable bearing system(not shown) which runs within a closed housing of the assembly 112 toguard against contamination. An integral hydraulic swivel system (notshown) allows continuous slip 114 operation without the need to connector disconnect hoses. The swivel features a cooling system (not shown) tominimise heat build up in seals (not shown) while the rotary bearingassembly 112 is being used for extended drilling operations. Preliminaryspecifications for the rotary bearing assembly 112 are as follows.

Compressive load rating 460,000 pounds Tense (snubbing) load 170,000pounds rating Rotational speed limit (swivel 106 rpm seal rating)Maximum swivel pressures (static 1500 psi non-rotating conditions) (notepressure should be bled off swivel while rotating) Maximum swivelcoolant pressure 60 psi Recommended swivel coolant supply 5–10 gpm flowrate

The swivel should be cooled by fresh water although glycerol basedantifreeze or equivalent may be required in cold climates.

A remote control and instrumentation console may also be provided andwhich features direct acting hydraulic control valves (not shown) toprovide control for the following:

-   i) Tong motor direction manual directional control which uses a    Danfoss PGV 120™ load independent proportional hydraulic control    valve assembly (not shown) for open loop power unit with a manual    lever operated valve section to control the tong motor with flow    rates to 47.6 gpm.-   ii) Tong motor mode (high torque, low speed or low torque, high    speed).-   iii) Tong torque limiter (manual preset for automatic dumping, and    an electronic solenoid can add computer dump control).-   iv) Tong backing pin.-   v) Hydraulic system pressure control.-   vi) Rotary back up motor manual directional control which uses a    hydraulic control valve assembly for open loop power unit with a    manual lever operated valve section. One section controls the rotary    back up 109 motors with flow rates to 145 gpm which is the maximum    allowable flow rate for continuous operation in high speed mode.    Infinitely variable rotational speed control may be achieved most    efficiently through the use of variable displacement pump systems.    Alternatively, the speed may be adjusted by throttling the direction    of control valve or through the use of an adjustable flow control    valve.-   vii) Rotary back up 109 motor mode providing for high torque, low    speed or low torque, high speed.-   viii) Tong backing pin for the rotary back up 109.-   ix) Braking system control.-   x) Torque gauge (hydraulic style) with dampener valve.-   xi) Hydraulic system pressure gauge.

Referring now back to FIG. 8 a, a tripping operation into an alreadydrilled borehole will now be described. By way of explanation, atripping operation is performed to insert tools required in the boreholefor a specific downhole operation.

With boreholes being many thousands of feet deep, the length of drillpipe 17 must be included in the drill string and inserted into theborehole as quickly as possible.

A make up/break out mechanism in accordance with the present inventionwill now be described.

FIG. 8 a shows the upper end of drill pipe 17 c projecting upwardly fromthe snubbing unit 20. At this point, the fixed slips 124, which arelocated within a fixed slip housing 3, are energised to firmly gripagainst the outer surface of the lower end of drill pipe 17 c, such thatthe fixed slips 124 are holding the entire weight of the drill string.The four hydraulic jacking cylinders 122 are then actuated to raise thesnubbing unit 20 upwards until it reaches the position shown in FIGS. 7a and 9 a, such that the upper end of drill pipe 17 c and lower end ofdrill pipe 17 b are located within the snubbing unit 20. The travellingslips 114 are then energised to engage the outer surface of drill pipe17 c just below the upper end thereof. The jaws of the rotary back up109 are then energised to engage the outer surface of drill pipe 17 cimmediately below the upper end thereof and the jaws of the upper tong108 are energised to engage the outer surface of drill pipe 17 bimmediately above the lower end thereof. The fixed slips 124 are thenreleased and the hydraulic jacking cylinders 122 are then actuated tomove the snubbing unit 20 downwardly. Simultaneously, the upper tong 108is operated to rotate drill pipe 17 b relative to drill pipe 17 c suchthat the two joints thereof are made up to the required torque level.Therefore, by the time snubbing unit 20 has reached the position shownin FIG. 10 a, the joint between drill pipe 17 b and 17 c has been madeup. The pipe handler fluid swivel 13 b can then be disengaged from theupper end of drill pipe 17 b and can be moved downwardly on the armrunner 9 b, as shown in FIGS. 11 b and 12 b to pick up another pipe 17.The fixed slips 124 are then re-energised to engage the outer surface ofdrill pipe 17 b, and when this has been done, the engagement betweenupper tong 108, rotary back up 109 and the respective drill pipe 17 b,17 c can be released. The hydraulic jacking cylinders 122 are thenactuated once more such that the snubbing unit 20 moves to theconfiguration shown in FIG. 13 a. The travelling slips 114 arere-energised to grip the drill pipe 17 and the fixed slips 124 arereleased. The hydraulic jacking cylinders 122 are then actuated to movedownwardly such that the snubbing unit 20 and travelling slips 114stroke the drill string 17 into the borehole. A typical length of travelof the hydraulic jacking cylinders 122, and hence stroke of the drillstring 17, is 13 feet. The snubbing unit 20 therefore moves from theconfiguration shown in FIG. 13 a to the configuration shown in the FIG.14 a and 15 a. Additionally, articulated pipe arms 12 a have moved pipe17 a to be co-axial with the drill pipe 17 b.

The fixed slips 124 are once again energised to engage the drill pipe 17b and the travelling slips 114 are released, such that the hydraulicjacking cylinders 122 move the snubbing unit 20 to the configurationshown in FIG. 16 a so that the upper end and lower end of respectivedrill pipes 17 b and 17 a are located within the snubbing unit 20.

This process is repeated for as many drill pipe 17 sections as requiredin order to make up the desired length of drill string 17.

This process provides an extremely quick make up (or if operated inreverse, break out) for a tripping operation.

Normally, for tripping operations, rotation of the drill string is notrequired. However, for drilling operations, the drill string 17 isrequired to be rotated and also requires that circulation occurs throughthe bore of the drill string 17 down to the drill bit located at thebottom of the drill string 17. The drilling rig 100 is capable ofimparting rotary movement to the drill string 17 without the requirementfor a conventional rotary table or top drive, and can also providecontinuous circulation through the bore of the drill string 17, as willnow be described.

The travelling slips 114, as previously described, are used to lower thedrill string 17 into, or raise the drill string 17 from, the borehole,and the control system for the hydraulic jacking cylinders can beoperated such that the cylinders 122 can push the drill string 17 intothe hole. For instance, the drilling operation may require that thedrill string 17 is forced down into the hole by a certain percentage ofweight of drill pipe 17, such as 10% weight. The rotary bearing assembly112 and the travelling slips 114 can also be operated to impart rotationto the drill string 17, either as it is being inserted into, or pulledfrom the borehole, or even whilst the drill string 17 is verticallystationary.

Additionally, or alternatively to the rotary bearing assembly providingthe power to rotate the drill string 17, the rotary backup 109 can beoperated to impart rotation to the drill string 17.

A continuous circulation apparatus and method in accordance with thepresent invention will now be described, which is particularly for useduring a milling/drilling operation.

FIGS. 18 to 23 show a portion of an apparatus 130 of the continuouscirculation system, with FIGS. 24 to 28 showing flow diagrams for theoperation thereof. FIG. 19 shows the continuous circulation apparatus130 in isolation, and FIG. 18 shows the continuous circulation apparatus130 incorporated in the snubbing unit 20. Referring firstly to FIG. 19,there is shown a first embodiment of apparatus 130 as comprising anupper seal 132 in the form of a shaffer sealing element 132, a lowerseal in the form of a pair of rams 134 a, 134 b and a middle full borevalve 136 in the form of a 10,000 psi plate valve 136. Housing for thesecomponents is also provided in the form of a shaffer type bonnet 138,centre housing 140 and a main housing 142. The shaffer seal 132 isprovided with a piston assembly 144 which can be moved upwardly toenergise the shaffer seal 132 around the outer surface of a pipe 17located in the bore of the shaffer seal 132 by the introduction ofpressured hydraulic fluid into sealed closed port 146. The pistonassembly 144 can be moved downwardly to release the sealing action ofthe shaffer seal 132 on the drill pipe 17 by introduction of hydraulicfluid into the seal open port 148.

It is important to note that the centre spindle 137 of the plate valve136 is not located on the intended path of the longitudinal axis of thedrill string 17. However, the main working plane of the plate valve 136is perpendicular to the longitudinal axis of the intended path of travelof the drill string 17. A pair of circular apertures 150 a, 150 b areprovided in the plate valve 136, and a pair of sealing rings 152 a, 152b are provided on the upper surface of the plate valve 136, such thatthe centres of the apertures 150 a, 150 b and sealing rings 152 a, 152 bare located at the same radius from the centre spindle 137. Furthermore,the centres of the apertures 150 a, 150 b are located on the samediameter, and the centres of the sealing rings 152 a, 152 b are alsolocated on the same diameter. The valve plate 136 is arranged such that,with the centre spindle 137 being off centre of the longitudinal axis ofthe drill string 17, the centre point of the apertures 150 a, 150 b andsealing rings 152 a, 152 b bisect the longitudinal axis of the drillstring 17 as the valve plate 136 rotates. In other words, the centrespindle 137 is located off centre by a distance equal to the radius ofthe centre lines of the apertures 150 and sealing rings 152.

As shown most clearly in FIG. 20, a circulating port 154 is formedimmediately vertically below the location of the plate valve 136 andimmediately vertically above the pipe rams 134 a, 134 b.

The inner faces of the pipe rams 134 a, 134 b are formed such that whenthe rams 134 are brought together, they provide a sealing fit around theouter surface of the drill pipe 17.

The plate valve 136 is provided with a gearing surface 156, and aninternal hydraulic motor 158 with an appropriately geared drive is alsoprovided, such that actuation of the hydraulic motor 158 rotates theplate valve 136.

Optionally, but preferably, a further port 220 (as shown in FIG. 24) isprovided into the inner chamber of the continuous circulation apparatus130, where the further port 220 is located in between the shaffersealing element 132 and the plate valve 136.

The further port 220 can be opened to purge air from the pipe joint 17Bbeing introduced into the apparatus 130 prior to the plate valve 136being opened; in this manner the shaffer seal 132 is first closed aroundthe pipe joint 17B and the further port 220 is opened such that air maybe flushed out or pumped out of the joint 17B.

Optionally, but preferably, a joint integrity checking apparatus isfurther provided for use with the continuous circulation apparatus 130;the joint integrity apparatus (not shown) provides an external pressurecheck on the integrity of the pipe joints that are made up within thecontinuous circulation apparatus 130. In order to utilise the jointintegrity apparatus, the pipe joint to be checked is maintained withinthe middle of the continuous circulation apparatus 130, that is in theposition shown in FIG. 25. The rams 134A, 134B are maintained in theclosed configuration, such that they seal about the upper end of thelower pipe 17C. Then, either a fluid or more preferably a gas, such asnitrogen or most preferably helium, is introduced under pressure intothe chamber (the portion intermediate the circulation port 154 andinjection port 184) through either the circulating port 154 or theinjection port 184 until the pressure of the fluid or gas reaches arelatively high fixed pressure. A pressure sensor (not shown), which ispreferably a digital pressure sensor, is provided in either thecirculating port 154 or the injection port 184 lines and the output ofthe pressure sensor is preferably coupled to a computer control systemthat is recording the whole activity of the rig 100; the computercontrol system typically being located in the rig cabin 31. The computercontrol system (not shown) monitors the output of the pressure sensor,such that if the output of the pressure sensor starts to fall then theintegrity of the pipe joint between the lower pipe 17C and the upperpipe 17B is questionable. Such a questionable pipe joint connectioncould be due to a number of factors such as, but not limited to:

-   1) wear and tear of the joint;-   2) contamination within the screw thread connections of the joint;-   3) insufficient torque being applied to the joint; and/or-   4) excessive jawing or washout passing through the joint on previous    trips of the joint into a borehole.

A second embodiment of a continuous circulating apparatus 160 is shownin schematic form in FIG. 26 and comprises an upper seal 162, which maybe in the form of a shaffer sealing element 162, similar to that shownin FIG. 19, a lower seal 164, again in the form of a shaffer sealingelement and a plate valve 166, similar to that shown in FIG. 19. Thisembodiment is termed a stripper design 160. With regard to the stripperdesign 160, it should be noted that the upper seal may alternatively bea rubber pack off element 162 in the form of a rubber ring 162. Thisprovides a friction seal with respect to the outside surface of the pipe17 or pipe joint and does not require to be actuated. The inner diameterof the rubber ring 162 is slightly less than the outer diameter of thepipe 17, and the rubber ring 162 is elastic such that it can deform toallow the passage of joints therethrough. The lower seal element 164 ofthe stripper design may have a similar rubber ring 164.

A third embodiment of a continuous circulating apparatus 170 is shown inFIGS. 27 and 28 and comprises an upper seal 172 in the form of a pair oframs 172 similar to the rams 134 shown in FIG. 19, a lower seal 174 inthe form of rams 174, similar to the rams 134 shown in FIG. 19, and acentre valve 176 in the form of a pair of full bore sealing rams 176.This third embodiment 170 is termed a ram design 170.

A method of operating the continuous circulating system will now bedescribed.

For drilling operations, the lower end of a kelly hose 180 is attachedto the upper end of the next drill pipe 17 to be made up into the drillstring, with the upper end of the kelly hose 180 being coupled to thepipe handler fluid swivel 13. A drilling fluid supply conduit 182 iscoupled to the outer end of the goose neck pipe 18. Referring to FIG. 9a, at this point in the circulation system cycle, no drilling fluid iscirculated through the goose neck 18, and the relative locations of thelower drill pipe 17 c and upper drill pipe 17 b within the snubbing unit20 is shown in schematic form in FIG. 24 at this point. Valve V₃, whichis located between the kelly hose 180 and the fluid supply conduit 182,is shown as closed. At this point, middle full bore valve, in the formof plate valve 136 is shown as being closed, in that one of the sealingrings 152 is concentric with the longitudinal axis of the drill pipe 17c. Lower valve 134 is closed around the outer surface of the upper endof drill pipe 17 c, and injection port 184 is closed by means of valveV₂. Valve V₄ is also closed and which is located between the kelly hose180 and a bleed off line 186. Valves V₅ and V₁ are located between thecirculating port 154 and the fluid supply conduit 182, and at thispoint, V₅ and V₁ are both open, and hence drilling fluid is beingsupplied through circulating port 154 and into the inner bore of thesnubbing unit 20 and hence inner bore of the drill pipe 17 c.

It should also be noted that the snubbing unit 20 is provided withanother slip system 190, in the form of upper slips 190, and which willnormally only be utilised during a continuous circulating operation. Theupper slips 190 (not shown in FIG. 17( a) but shown in schematic form inFIGS. 24 and 25, and shown in a preferred form in FIGS. 29, 30 and 31)are mounted to the upper end of a feeder plate 192 of the snubbing unit20 by means of an arrangement of hydraulic jacking cylinders 194, and ina preferred embodiment, there are four such hydraulic jacking cylinders194. The upper slips 190 are operable to firmly grip the drill pipe 17 bas it is being inserted into the snubbing unit 20, such that the upperslips 190 provide support to the drill pipe 17 b, and the hydraulicjacking cylinders 194 are actuated to firmly lower or feed the drillpipe 17 b into the snubbing unit 20.

The next stage of operation is shown in FIG. 25, and which shows thatthe middle plate valve 136 has been rotated such that an aperture 150 isco-axial with the longitudinal axis of the drill pipes 17.Simultaneously, the upper seal 132 is closed around the upper pipe 17 b,and valve V₃ is opened. This flushes fluid into the drill pipe 17 b andhence equalises the pressure above the plate valve 136 with the pressurebelow the plate valve 136, since valves V₅ and V₁ are still open.

The upper slips 190 remain actuated to firmly grip, and hence support,the drill pipe 17 b against the force of the pressure which wouldotherwise force the drill pipe 17 b upwards and out of the snubbing unit20.

The plate valve 136 is then rotated to the position shown in FIG. 25such that one of the apertures 150 is concentric with the longitudinalaxis of the drill pipe 17. Valve V₁ is then closed.

Downward movement of the upper pipe 17 b is again commenced aspreviously described (i.e. by a combination of downward movement of thewire pulley 10 b and also downward movement of the hydraulic jackingcylinders 194) until it comes into close proximity with the upper end oflower pipe 17 c. Valve V₂ is then opened and a suitable fluid issupplied into the injection port 184 via the now open V₂, in order toflush the threads of the two pipes. Hence, the upper tong 108 and thelower tong or rotary back up 109 are operated to grip the two pipes 17b, 17 c and the actuation of the upper slips 190 upon the drill pipe 17b is released. Thereafter, the upper tong 108 and the lower tong/rotaryback up 109 are operated to make up the two pipes 17 b, 17 c.

The drill string 17 continues its downward movement by operation of thehydraulic jacking cylinders 122, travelling slips 114 and fixed slips124 until such a time that the upper end of the pipe 17 b is at thethread engagement height; that is the location of pipe 17 c as shown inFIG. 24. The kelly valve is then backed off the upper end of pipe 17 band is pulled upwardly by the counterbalance winch and/or the upperslips 190 and hydraulic jacking cylinders 194. It should be noted thatupper seal 132 is still sealing around the kelly valve. Once the kellyvalve has passed upwards through the aperture 150, the middle platevalve 136 is closed. Valve V₄ is then opened to bleed off pressure, andV₃ is closed and V₅ is opened. The upper seal element 132 can then beopened and the next pipe joint can be introduced into the snubbing unit20. The method is repeated for as many joints as required, and hencecontinuous circulation of drilling fluid through the drill string isachieved.

FIGS. 29 to 31 show a preferred form of a slip mechanism 200; it shouldbe noted that the slip mechanism 200 is preferably suitable for use asthe fixed/stationary slips 124 and/or travelling slips 114 and/or upperslips 190.

The slip mechanism 200 can also be referred to as a snubbing slipmechanism 200. The slip mechanism 200 comprises a slip bowl 202 or sliphousing 202 which is provided with at least one, and preferably four,hydraulic jacking cylinders 204 which extend vertically upwardly fromthe base of the slip housing 202. Four snubbing slips 206 are providedwithin the slip housing 202 where the width of each snubbing slip 206circumscribes no greater than 90° of a circle. The innermost faces ofeach of the snubbing slips 206 have a common curvature such that whenthey are in the closed configuration as shown in FIG. 30, they 206 cometogether to form an inner bore and are provided with a suitably gripablesurface such that they 206 are capable of securely gripping the outersurface of the drill pipe 17 and can thus support the weight of thedrill string.

The inner surface of the slip housing 202 is tapered outwardly from thebase of the slip housing 202 to the uppermost portion of the sliphousing 202 and four longitudinally extending slots (not shown) areformed equi-distantly around the inner surface of the slip housing 202.A longitudinally extending dovetail shaped key (not shown) is providedon the outer surface of each snubbing slip 206 such that the dovetailshaped key engages in the respective slot of the slip housing 202. Theupper end of the hydraulic jacking cylinders 204 are suitably coupled toeach snubbing slip 206 such that actuation of the hydraulic jackingcylinders 204 moves the cylinders 204 from their home (non-stroked)configuration shown in FIG. 30 to the fully stroked configuration shownin FIG. 29; in this manner the snubbing slips 206 can be moved from theclosed (and pipe gripping) configuration shown in FIG. 30 to the open(and non-pipe gripping) configuration shown in FIG. 29.

It should be noted that conventionally, particularly when tubing such ascasing and liner tubing (which has a flush outer surface along itslength) is being passed through a set of slips, that a safety mechanismis used. This conventional safety mechanism comprises a manual clampwhich is set around the outer surface of the tubing and which must beput on manually by an operator such as a roughneck. This manuallyapplied clamp is arranged to act as a safety feature such that if thesnubbing slips 206 lose their grip on the smooth outer surface of thecasing/liner string then the manually applied clamp will collide againstthe upper surface of the snubbing slips, thus forcing them further downthe tapered surface and thereby increasing the grip being applied by thesnubbing slips to the outer surface of the casing. However, thisconventional clamp arrangement is dangerous to apply and also timeconsuming.

In accordance with the present invention a safety slip 208 is mounted tothe upper end of each snubbing slip 206 by means of a biasing mechanismsuch as a set of coiled springs 210; however, those skilled in the artwill appreciate that a different type of biasing mechanism could beused, such as a leaf spring or rubber/neoprene element (not shown) or alever arrangement as shown in the second embodiment of FIGS. 32 to 34.The coiled springs 210 are arranged to naturally bias the safety slips208 away from the snubbing slips 206. When the snubbing slips 206 are inthe closed configuration as shown in FIG. 30, they are gripping thecasing string or drill string 17 and the safety slips 208 are alsogripping the outer surface of the string since the rear end or outermostend of each safety slip 208 abuts against a safety slip stop 212 whichis conveniently mounted in a suitable manner to the upper end of thesnubbing slip 206. Even more advantageously, the safety slip 208 isprovided with a moveable safety slip front 214, where the safety slipfront 214 is mounted to the safety slip back 208 by means of a dovetailshaped key (not shown) and slot (not shown) arrangement provided on atapered surface, as shown in FIG. 31.

Accordingly, with the safety slip front 214 gripping the casing string,if the casing string begins to slip through the snubbing slips 206 whenthey are in the closed configuration, the safety slip front 214 and thenthe safety slip back 208 will travel downwardly with the casing stringagainst the biasing action of the coiled springs 210 until the lowerface of the front 214 and back 208 collide with the upper face of thesnubbing slips 206 across the full cross-sectional area of the upperface of the snubbing slips 206 (which are greater in cross-sectionalarea than the lower face of the snubbing slips 206). Accordingly, theaforementioned collision causes the snubbing slips 206 to movedownwardly to grip the tubing string even more. When the tubing stringor drill string is ready to intentionally move through the slipmechanism 200, the cylinders 204 are actuated to stroke outwardly fromthe closed configuration of FIG. 30 to the open configuration of FIG.29. In this manner, the snubbing slips 206 and safety slips 208, 214 aremoved not only upwardly but outwardly away from the tubing/drill string17, and the safety slips 208, 214 are moved upwardly away from thesnubbing slip 206 by the biasing mechanism 210, such that they 208, 214return to their 208, 214 starting (spaced) configuration.

Accordingly, the embodiment of the slip mechanism provides an automaticsafety slip 208, 214 device that does not require manual intervention.

FIGS. 32, 33 and 34 show an alternative arrangement of the safety slips208, 214 where the safety slips 208, 214 move in an arc via a hinge 218and pivot 219 into engagement and out of engagement with the tubingstring or drill string 17, rather than in the vertical movement shown inthe embodiment of FIGS. 29 and 30, where the arc movement is shown inFIG. 33 by arrow 216. In addition, the hinge 218 that moves about thepivot 219, acts as a safety slip stop 218, 219.

The aforementioned apparatus provides distinct advantages overconventional work over and drilling units. For instance, it is capableof making or breaking connections while circulating and tripping pipe inor out of the well bore. Furthermore, it can replace a conventionalrotary table and can be rigged up on almost any drilling rig, platform,drill ship or floater. For rig assist, the jacking slips are picked uplike a joint of pipe and simply stabbed into the rotary table. The unitfits flush with the rig floor and allows for normal rig pipe handling tobe used. In this scenario, there is minimal or no learning curve for therig personnel to go through, and with there being no loose equipmentabove the rig floor 8 associated with this apparatus, the possibility ofdropped objects has been eliminated.

The unique articulating pipe handling arms 12 and power tong 108, 109make up provides the apparatus 100 with the ability to make tubularconnections “on the fly” with a continual trip speed of over 60 jointsper hour being possible.

The apparatus 100 can be broken down into readily liveable components.Furthermore, the continuous circulation feature allows an operator tomake and break connections without stopping circulation of fluid throughthe drill string. It is envisaged that the system will minimise collapseof boreholes and differential sticking without surging the boreholeformation.

Modifications and improvements can be made to the embodiments hereindescribed without departing from the scope of the invention.

1. A method of circulating fluid through a tubular string, the string comprising at least one tubular, the method comprising: providing a first fluid conduit for supplying fluid to the bore of an upper tubular to be made up into or broken out from the tubular string; inserting the lower end of the upper tubular into an upper port, where a valve mechanism denies the flow of fluid into the first fluid conduit; gripping the upper tubular with an upper tong; selectively rotating the upper tubular; providing a second fluid conduit for supplying fluid to the bore of the tubular string; gripping the tubular string with a lower gripping device; and selectively rotating the tubular string with the lower gripping device.
 2. The method according to claim 1 comprising the further including operating the valve mechanism to permit the flow of fluid into the first fluid conduit and upper end of the tubular.
 3. An apparatus for circulating fluid through a tubular string, the apparatus comprising: a first fluid conduit for supplying fluid to the bore of an upper tubular to be made up into or broken out from the tubular string; a second fluid conduit for supplying fluid to the bore of the tubular string; a first gripping device for gripping the upper tubular, the first gripping device capable of providing rotation to the upper tubular; a second gripping device for gripping the tubular string as the first gripping device provides rotation to the upper tubular; and a tubular movement assembly capable of moving the tubular string relative to the first gripping device and the second gripping device, wherein the tubular movement assembly comprises a third gripping device, a fourth gripping device and a motive member for moving the third gripping device relative to the fourth gripping device.
 4. The apparatus of claim 3, wherein the motive member is a fluid cylinder.
 5. The apparatus of claim 3, wherein the third gripping device is capable of rotating with the tubular string.
 6. The apparatus of claim 3, wherein the third gripping device is capable of being remotely operated.
 7. An apparatus for providing a continuous circulation through a tubular string, comprising: a chamber having a rotatable plate valve disposed therein, the rotatable plate valve providing a selective communication pathway between an upper portion and a lower portion of the chamber; a first fluid conduit for supplying fluid to a tubular to be made up into or broken out from the tubular string, the first fluid conduit in fluid communication with the upper portion; a second fluid conduit in fluid communication with the lower portion for supplying fluid to the tubular string; an upper tong having a gripping device for gripping the tubular, the upper tong further comprising a rotation mechanism to provide rotation to the gripping device to provide rotation to the tubular; and a lower gripping device for gripping the tubular string.
 8. The apparatus of claim 7, wherein a center of the rotatable plate valve is misaligned with a center of the tubing string. 